The only reason I can possibly think of is mob mentality. I'm very glad I bought it, it broke me out of a gaming slump I've had for years.
Agreed, it's had a very shoddy release, and i'm glad i only paid ~£25 for it, as i think i'd have been pretty miffed at paying £40 considering the number of bugs that were present on day 1.
However Bethesda are getting their act together and have fixed a large number of these, and i believe there's also another patch planned for Tuesday.
I think most people are jumping on the anti-multiplayer bandwagon, which actually isn't as big of a deal as people are making out. This isn't some MMORPG where there's hundreds/thousands of players on a server, you'll bump into players for certain events, especially exploring blast zones after a nuke has just been dropped. But for most of the time, it's pretty uncommon to bump into other players. There's also plenty of side quests, so arguing that lack of NPC's doesn't give much of a story, isn't quite true.
I'm thoroughly enjoying the game (despite running into a few issues), and whilst looks/feels are very similar to Fallout 4, it's a completely different game. FO76 is very much focused on the survival aspect, and means you're very limited in things you can carry around with you, or store. It means you have to think about what weapons you don't/won't actually use, and what junk components you might need lots of.
With how much the game has come down in price, i think people would be mad not to give it a go.